I've got the feeling that some people confuse "using spanking when necessary" with "spanking children as many times as you can".
I've been spanked when I behaved bad. In the ten years during which it happened, it happened less than what you can count on one hand (I remember two times myself, maybe three).
If you really believe that a slap on the butt once every three years is going to damage a mind, you may be much closer to be mentally damaged than the poor children being spanked.
Spanking the children so often that he becomes desensitivized is something else entirely.